code: def test_multi_agent_invalid_sub_values(self):
      self.assertRaisesRegex(
          ValueError,
          "config.multi_agent\\(count_steps_by=..\\) must be one of",
          lambda: (
              PPOConfig().multi_agent(count_steps_by="invalid_value")
          ),
      )
  
file_path: ray/rllib/utils/tests/test_check_multi_agent.py
imports: import unittest
  from ray.rllib.algorithms.ppo import PPOConfig
  from ray.rllib.policy.policy import PolicySpec
label_desc: Use image node_id 3 for calling the TestCheckMultiAgent obj's underlying member method code with example usage: obj.test_multi_agent_invalid_sub_values() without return types